Anais da IX Conferência Internacional de Proteínas e Coloides Alimentares

Essential oils are natural preservatives rich in compounds with antimicrobial and antioxidant properties, which can be applied in the form of emulsions in active coatings aiming at improving foods’ shelf life. Droplet size reduction to the nanoscale (< 200 nm) may improve emulsion stability, transparency, and antimicrobial activity. In the case of high-moisture foods, such as fish and meat, alginate-stabilized emulsions are a good alternative to be applied in active coatings, since they can turn into gels when reticulated by divalent cations. The objective of the study was to develop alginate-based nanoemulsions of three types of essential oils (thyme (Thymus vulgaris), lemongrass (Cymbopogon citratus), and oregano (Origanum vulgare)), with potential to be applied in active coatings and films, and to compare their physical properties with conventional emulsions. Essential oils’ chemical composition (GC-MS), antioxidant capacity (TEAC), and antimicrobial activity against Salmonella Typhimurium and Pseudomonas aeruginosa were investigated. Three coarse emulsions of each oil (thyme: T-CE, lemongrass: L-CE, and oregano: O-CE) containing water, sodium alginate (1%), essential oil (1%), and Tween 80 (1%) were prepared using an Ultra-Turrax at 10,000 rpm for 3 min; these emulsions were then homogenized with an ultrasonic probe (1 min/150 W) in order to produce the nanoemulsions (thyme: T-NE, lemongrass: L-NE, and oregano: O-NE). Oil droplet size, polydispersity index, and zeta potential were evaluated in the nanoemulsions and their respective emulsions. Thymol (44%), Geranial (43.7%), and Carvacrol (70.9%) were the main components of thyme, lemongrass and oregano, respectively. Oregano showed a higher antioxidant capacity (278,068 µmol TE/100 g oil). All oils showed antimicrobial activity against Salmonella Typhimurium and Pseudomonas aeruginosa. Size analysis indicated that T-CE, T-NE and L-NE were in the nanoscale and the ultrasound treatment significantly reduced the mean oil droplet of lemongrass samples (L-CE: 585 ± 44 nm vs L-NE: 147 ± 15 nm). The distinct effect of ultrasound treatment on samples droplet size could be related to the oils’ varied chemical composition. Each oil has a specific affinity with the applied emulsifier, which affect its ability to reduce interfacial tension, inhibiting droplet disruption. Ultrasound treatment reduced the polydispersity index in thyme (T-CE: 0.48 ± 0.03 vs T-NE: 0.39 ± 0.06) and lemongrass (L-CE: 0.49 ± 0.04 vs L-NE: 0.40 ± 0.04) nanoemulsions, suggesting that this high-energy homogenization method was able to reduce oil droplet size variations. O-CE (-58 ± 3 mV) and O-NE (-59 ± 3 mV) showed the highest zeta potential, while L-CE (-45 ± 3 mV) showed the lowest one, which can be also attributed to the oils distinct chemical composition that could influence oils droplets charges. Ultrasound treatment did not affect samples’ zeta potential. Oils characterization indicated their potential use as active ingredients in the development of alginate-based active coatings with antioxidant and antimicrobial activity. Ultrasound treatment reduced L-NE oil droplet size and promoted a more homogeneous oil droplet size distribution in thyme and lemongrass samples. The next steps include the investigation of nanoemulsions’ physical and chemical properties, antimicrobial activity, and application in fish fillets after alginate reticulation.